Evolution of the initial hole in vertically vibrated shear thickening fluids

Abstract

The apparent viscosity of shear thickening fluid (STF) changes dramatically with the applied shear rate, which is a typical rheological property of STF. Such a rheological property affects the vertically vibrated dynamic property of STF. In order to get a better understanding of the vertically vibrated dynamic properties of STF, the surface instabilities in vertically vibrated STF, which was prepared by suspending polymethylmethacrylate particles in ethylene glycol, are investigated. Above a critical driving acceleration, the surface instability transforms from the disappearance to the fission of the initial hole, which is produced by applying a finite perturbation to the surface. The time required for the initial hole to disappear can be affected by the driving acceleration, vibration frequency, volume fraction, thickness, and shape and size of the perturbation. A possible model is proposed, and the expressions of hydrostatic force and viscous dissipative force are employed to clarify the relationship between disappearance of the hole and shear thickening effect. The fission and spreading follow a hexagonal arrangement. At a higher acceleration, the holes cover the entire surface in a state of disorder. The mechanism for the initial hole's evolution in vertically vibrated shear thickening fluids is discussed.